Queen Camilla will miss some elements of the Qatari state visit this week due to a viral chest infection, a Buckingham Palace source says.

A Palace source said that the infection she has had in recent weeks is lingering, leaving her with diminished reserves of energy.

Changes to the Queen’s programme have been made on the advice of doctors.

The 77-year-old will now not attend the official arrival of the Emir of Qatar on Tuesday morning and her presence at other elements of the visit will be scaled back.

King Charles and the Prince and Princess of Wales are set to welcome the Qatari leader to the UK during the traditional formal greeting at London's Horse Guards Parade.

It will be the first state visit that Catherine will participate in since her cancer diagnosis, which was announced in March, as part of her gradual return to public duties.

The Queen will not be present for a carriage ride back to Buckingham Palace after the traditional formal welcome.

She will attend a lunch at the palace when the royal party returns and is hoping to see an exhibition in the Picture Gallery inthe royal residence.

The Queen will also attend the state banquet on Tuesday but Catherine will miss that event.

She is expected to be at the farewells to the emir on Wednesday.

Palace sources say the diagnosis she initially received in November has not changed and she needs time to rest and recover fully, which is more challenging with the back-to-back nature of engagements on a state visit.

The engagements changed for the state visit would have involved the Queen spending a considerable amount of time outside or standing and greeting people.

With temperatures expected to hover around 7C in London on Tuesday, it is likely royal doctors were keen for the Queen to miss the ceremonial welcome to avoid her standing in the cold for an extended period of time.

The Queen contracted the illness a month ago after a trip with the King to Australia and Samoa, which included a stopover in India on the way back.

Announcing the infection in early November, Buckingham Palace said: "Her Majesty The Queen is currently unwell with a chest infection, for which her doctors have advised a short period of rest."

She pulled out of a number of scheduled engagements at the start of November - such as Remembrance Sunday, because of the chest infection and doctors had advised she spend a short period of rest at home.

The Palace said she would return to public duties later that month but with some changes to her schedule.

She appeared at an event at the University of London, where she was presented with an honorary doctorate of literature by Princess Anne.

The Queen did not attend the Royal Variety Performance with the King on 22 November after the Palace announced she would not be joining him following "lingering post-viral" symptoms from the chest infection.